It’s taken the musical “Cats” nearly 40 years to make its way from the stage to the big screen. Now we know why.

Just as there are some novels that defy dramatization, so there are stage productions that derive their power from the interaction of audience and performer, that work precisely because the viewer realizes that all the magic unfolding in front of him/her is being created by real people in real time.

Tom Hooper’s movie version, on the other hand, has been so digitally diddled with that we can’t be sure that anything we’re seeing — from the settings to the performers’ faces — is even remotely real. Characters do impossible flips in the air, cockroaches march in formation…it’s all so artificial that the film might as well have been done as pure animation (actually that was the plan, back in the ’90s).

That said, the movie “Cats” isn’t a total wipeout. The score (the tunes are by Andrew Lloyd Webber, the lyrics derived from T.S. Eliot’s book of poems Old Possum’s Book of Practical Cats) remains humworthy and at least a couple of the performers manage to transcend their hairy makeup (all too often they look like werewolves from a ’60s Hammer film) and establish an emotional connection with the audience.

A big problem is that “Cats” lacks a real story. On stage this wasn’t a deal breaker…the show was a musical revue with different “cats” taking center stage to sing and dance their signature numbers. What plot there was dealt with the approaching Jellicle Ball where one lucky feline will be chosen by the ancient Deuteronomy to be reincarnated into a new life (cats get nine of them, after all).

The screenplay by Lee Hall and Hooper centers on Victoria (ballerina Francesca Hayward, who seems capable of expressing only a quizzical attitude), abandoned by her owner in a dirty alley and adopted into the Jellicle tribe. Her guide and guardian is Munkstrap (Robbie Fairchild), who introduces her to various other characters and the rundown corner of London they call home.

In recent years even Spike Lee’s biggest fans may have wondered if the creator of “Do the Right Thing” was circling the drain of irrelevancy.

Worry no more. Lee — with an assist from the University of Kansas’ Kevin Willmott and the long-dead playwright Aristophanes — has come roaring back with “Chi-Raq,” a passionate indictment of black-on-black urban violence.

It’s a swing-for-the-bleachers effort that is by turns furious, raunchy, sad, silly and savage.

This mashup of rap concert, poetry reading (the bulk of the dialogue is in rhyming verse) and burlesque sometimes slips into preachiness or heavy-handed satire, but even the shortcomings become part of the film’s overall strength.

“Chi-Raq” begins with titles informing us that in recent years there have been more gun deaths among the citizens of the Windy City than among our special forces fighting in Iraq and Afghanistan.

Then Nick Cannon’s furious rap “Pray 4 My City” kicks in as a sort of profane overture: “Y’all mad cause I don’t call it Chicago / I don’t live in no *** Chicago / Boy, I live in Chi-Raq.”

The city’s South Side is torn between two gangs, led by the preening, cocksure Chi-Raq (Cannon) and the one-eyed, comically goofy Cyclops (Wesley Snipes).

When a little girl dies in a gang crossfire, Chi-Raq’s girlfriend, Lysistrata (Teyonah Parris of “Dear White People”), is so moved by the sorrow and anger of the girl’s mother (Jennifer Hudson) that she organizes the women of both gangs into a movement.

They will deny their men all sexual favors until the guns are put away and violence renounced. Pretty soon their message is taken up by women all over the world. Hookers stop hooking. Porn stars stop porning.